Digital Signal Processing Reference
In-Depth Information
Example 4.5 and PSpice Example
* Specify input source:
Vs 11 0 AC 1 0
* Stage Number 1
(Practical Values)
R11 11 12 1.155E+04
(1.15E+04)
C11 12 0 1.000E-07
(1.00E-07)
Rb1 13 21 1.000E+00
(1.00E+00)
X1 12 13 21 OPAMP
* Stage Number 2
C21 21 22 1.000E-07
(1.00E-07)
C22 22 24 1.000E-07
(1.00E-07)
C23 23 0 2.000E-07
(2.00E-07)
R21 21 23 5.046E+03
(4.99E+03)
R22 23 24 5.046E+03
(4.99E+03)
R23 22 31 2.523E+03
(2.49E+03)
Ra2 25 0 1.000E+04
(1.00E+04)
Rb2 25 31 2.913E+04
(2.94E+04)
Co2 24 0 2.620E-07
(2.70E-07)
X2 24 25 31 OPAMP
* Stage Number 3
C31 31 32 1.000E-07
(1.00E-07)
C32 32 34 1.000E-07
(1.00E-07)
C33 33 0 2.000E-07
(2.00E-07)
R31 31 33 3.118E+03
(3.09E+03)
R32 33 34 3.118E+03
(3.09E+03)
R33 32 41 1.559E+03
(1.54E+03)
Ra3 35 0 1.000E+04
(1.00E+04)
Rb3 35 41 4.863E+04
(4.87E+04)
Co3 34 0 6.860E-07
(6.80E-07)
X3 34 35 41 OPAMP
* Voltage divider section
Rx 41 42 2.294E+05
(2.32E+05)
Ry 42 0 1.046E+04
(1.05E+04)
* Sub-circuit model for op-amp
.SUBCKT OPAMP 1 2 6
Ri 1 2 1.000E+08
E1 3 0 1 2 1.000E+03
Rx 3 4 1.000E+03
Cx 4 0 1.000E-09
E2 5 0 4 0 1.000E+03
Ro 5 6 1.000E+00
.ENDS
* Analysis modes
.AC DEC 100 1.000E+01 1.000E+03
.PROBE
.END
Listing 4.1
Circuit analysis data file for Example 4.5.
The next step in the testing of the active filter is to replace the ideal
components with practical values. For this exercise, we will use 1% resistor and
2% capacitor values. (The selected values are shown in italics and parentheses in
the listing.) A worst-case analysis can then be run on the circuit that involves
adding tolerance information for the component values. (You need access to the
PSpice program to make this run.) During the worst-case analysis, sensitivities for
each component are determined, and as the final step, each component is set to its
worst-case extreme. Figure 4.16 shows both the worst-case and nominal response.
